Process for the thermal degradation of rubber containing waste

ABSTRACT

A process for the non-oxidative thermal degradation of a rubber containing waste including: transporting the rubber containing waste along a horizontal axis of a hermetically sealed cylindrical reactor including: an inlet and an outlet, one or more thermal reaction zones arranged between the inlet and the outlet, wherein each thermal reaction zone is provided with: one or more heating elements controllable to heat the thermal reaction zone to an operating temperature for mediating the non-oxidative thermal degradation of rubber in the rubber containing waste, and one or more gas outlets for withdrawing volatile gas or gases evolved during the non-oxidative thermal degradation of the rubber; and a screw auger located within the reactor, the screw augur configured to rotate in both the forward and reverse directions to agitate and transport the rubber containing waste through the one or more thermal reaction zones in both the forward and reverse directions and to the outlet; heating the rubber containing waste, in the one or more thermal treatment zones, to a temperature above the degradation temperature of rubber for a time sufficient to produce the volatile gas or gases and the char product; operating the screw auger in both the forward and reverse directions to agitate the rubber containing waste within the reactor; and advancing the rubber containing waste along the horizontal axis to the outlet.

PRIORITY CLAIM

This is a continuation of U.S. Non-Provisional application Ser. No.16/467,554, filed Jun. 7, 2019, titled “PROCESS FOR THE THERMALDEGRADATION OF RUBBER CONTAINING WASTE,” which is a 35 U.S.C. 371National Stage of International Application No. PCT/AU2017/051357, filedDec. 8, 2017, titled “PROCESS FOR THE THERMAL DEGRADATION OF RUBBERCONTAINING WASTE,” which claims priority to Australia Application No.2016905092, filed Dec. 9, 2016, the disclosures of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention is directed towards a process for the thermaldegradation of a rubber containing waste.

BACKGROUND OF THE INVENTION

Each year, millions of tonnes of waste rubber products are discarded.One of the primary and most problematic sources of this waste rubber isused tyres. These tyres may be from: on road vehicles ranging frombicycle tyres, motorcycle tyres, car tyres and heavy vehicle tyres;agricultural vehicle tyres; industrial tyres such as for aircraft,forklifts tyres and OTR and Haul pack tyres in the mining sector. Othersources of waste rubber include: industrial waste, such as conveyorbelting; and consumer market scrap rubber from the manufacture ofproducts such as but not limited to footwear, furniture, medical wasteand many other domestic and commercial products. Historically much ofthis rubber waste ends up in landfill, such as in tyre disposal yards.

Given the significant amounts of rubber waste that is generated eachyear, there is substantial interest in finding an economic andenvironmentally sustainable solution for dealing with the rubber waste.

As indicated above, the primary and most problematic source of rubberwaste is in the form of used tyres. A used tyre carcass is composed ofseveral parts, including: the tread, the bead, and the sidewall.

The tread is the part of the tyre that contacts road surfaces, and assuch is the component that becomes worn during use leading to the tyrebeing discarded. The tread consists of a thick rubber composite compoundand is formulated to provide an appropriate level of traction and isdesigned not to wear away too quickly. The rubber may be natural orsynthetic, and may additionally include carbon black and numeroushydrocarbon-based chemicals. Various types and blends of rubbers areused in the manufacture of tyres with the most common beingstyrene-butadiene copolymer. The tread pattern imprinted on tyres ischaracterised by a geometric shape of grooves lugs, voids and sipes. Allfeatures on the tread surface of a tyre are designed to allow water toescape from between the tyre and the traction surface to preventhydroplaning, or in the case of OTR tyres, to promote traction with thesurface they are coming in contact with. Immediately under this treadsection of tyre is various reinforcing material, sometimes, thismaterial only consists of a cloth or nylon type fabric. Commonly foundis a woven steel fabric vulcanised into the rubber. This vulcanisationprocess makes it difficult to recycle used tyres.

The bead is vulcanised steel reinforcement designed for tyre supportthat comes in contact with the rim on the wheel. The bead is typicallyreinforced with a high-grade high tensile steel wire and a lowflexibility rubber. The bead seals tightly against the two rims on thewheel to ensure that in the case of a tubeless tyre that the tyre holdsair without leakage. The bead is designed to fit snugly and tight toensure that the tyre does not rotate circumferentially as the wheelrotates.

The side wall is a part of the tyre that bridges between the bead andthe tread. The side wall is proportionally composed largely of rubberbut will often have reinforcing fabric or fine steel meshes and fibresvulcanised in its construction which provide tensile strength andflexibility. The main purpose of the sidewall is to contain air pressureand transmit torque applied from the drive axle to the traction circlebelow the tread.

Recently, there has been a move to recycle waste tyres by repurposingthem or converting them into other products. In some instances the tyrescan be used whole. However, this approach is inadequate for dealing withthe substantial amount of waste tyres that are produced each year.

Another approach is the physical fragmentation of the tyres into piecesof varying sizes by some physical means such as the use of shreddersand/or the use of hammer mills or granulation, then once the wasterubber is broken up, in most cases the steel wires and steel fragmentsare removed along with any nylon or fibreglass contamination and thenthe rubber is re-claimed to produce a recycled rubber product. Often thepoor quality of this recycled rubber product due to the blending ofsynthetic and natural rubber renders it unsuitable for use as a rawmaterial to produce new rubber (e.g. for use in the manufacture of newtyres). Instead, this fragmented and processed rubber is used in theformation of products that can tolerate large variances in the rubber'schemical make up in their manufacture in such cases they are oftenbonded with adhesives or solvents to form the end product, such as butnot limited to the manufacture of rubber matting, soft fall surfaces,athletic track surfaces and many other sporting facilities along withchild playground equipment surfaces or padding. These approaches are notwithout their downsides. They are inadequate for dealing with largevolumes of waste tyres. Furthermore, they give rise to environmentalproblems due to the potential for heavy metals to leach out andcontaminate ground water. Additionally, the metal containing fraction isoften discarded to landfill as the cost and difficulty associated withseparating the woven steel fabric from the remaining rubber isprohibitive.

A further approach involves digestion of the rubber using a chemicalprocess. Following physical fragmentation of the rubber it is added to achemical solution of cellulose degrading and destroying chemicals suchas sodium hydroxide or zinc chloride or other solvents to break therubber down into smaller organic molecules. Drawbacks and problems withthe chemical degradation of rubber are numerous but primarily theprocess suffers from being uneconomical, and the requirement for furthertreatment and/or disposal of the resultant chemicals gives rise toenvironmental concerns.

Another approach to disposing of waste tyres is through pyrolyticdegradation. Tyre pyrolysis involves heating a batch of waste tyres inan oxygen-free atmosphere to degrade the rubber in the waste tyres intosmaller organic molecules. These smaller molecules are typically formedin the vapour phase, and can be condensed for recovery. This batchpyrolysis process is generally operated at high temperature, generallyat 1400° C. or greater, to promote the formation of fuel oil products,such as those in diesel. This requires a substantial amount of heatenergy. The minerals that formed part of the tyre, around 40% by weight,are converted to ash or char. This ash or char is generally consideredto have little or no commercial value. Tyre pyrolysis is generallyconsidered uneconomical due to the large energy requirements and the lowvalue of the output products.

In view of the above, there is a need for a commercially viablemechanism for dealing with waste tyres that is environmentally sound.

Reference to any prior art in the specification is not an acknowledgmentor suggestion that this prior art forms part of the common generalknowledge in any jurisdiction or that this prior art could reasonably beexpected to be understood, regarded as relevant, and/or combined withother pieces of prior art by a skilled person in the art.

SUMMARY OF THE INVENTION

There is disclosed herein a hermetically sealed flow-through reactor fornon-oxidative thermal degradation of a rubber containing waste into achar product, the reactor having an internal cylindrical surface, andthe reactor including:

an inlet and an outlet,

one or more thermal reaction zones arranged between the inlet and theoutlet, wherein each thermal reaction zone is provided with:

-   -   one or more heating elements controllable to heat the thermal        reaction zone to an operating temperature for mediating the        non-oxidative thermal degradation of rubber in the rubber        containing waste, and    -   one or more gas outlets for withdrawing gas or gases evolved        during the non-oxidative thermal degradation of the rubber; and

a screw auger located within the reactor, the screw augur configured torotate in both the forward and reverse directions to agitate andtransport the rubber containing waste through the one or more thermalreaction zones in both the forward and reverse directions and to theoutlet,

-   -   wherein flighting on the screw auger tracks the internal        cylindrical surface of the reactor in close relationship to        minimise or prevent the transport of material through a        clearance space between outer edges of the flighting and the        internal cylindrical surface of the reactor.

In an embodiment, the screw augur is controllable to rotate in both theforward and reverse directions.

Typically the output char product includes carbon ash, and steel, whichmay later be separated.

In one form, the reactor has a cylindrical reactor body, such as in theform of a sheet metal or plate metal shell (which may be formed, forexample, from 16 mm or 32 mm sheet steel), the cylindrical reactor bodyhaving an internal cylindrical surface and an external cylindricalsurface. The presence of an external cylindrical surface is advantageouswhere the heating elements are provided in the form of band heaters.

In one form, the reactor is oriented substantially horizontally, suchthat the reactor has a horizontal axis along which the rubber containingwaste is transported by the screw auger.

The thermal reaction zones mediate the non-oxidative thermal degradationof rubber in the rubber containing waste. This is intended to mean thatthese thermal reaction zones are controlled to advance the degradationof rubber in the rubber containing waste into rubber depolymerisationproducts. To this end, the thermal reaction zones are provided with: atleast one heating element to provide heat to the reaction zone to heatthe rubber above its thermal degradation temperature; and gas outletsfor extracting volatile depolymerisation components. The heatingelements and gas outlets may be operated and controlled such thattemperature and negative pressure (such as below atmospheric pressure)is applied to the thermal reaction zone to affect the thermaldegradation reaction. The term “negative pressure” is intended to referto a pressure that is below atmospheric pressure.

Preferably the rubber containing waste is tyre waste, such as strippedor shredded tyre waste. More preferably the rubber containing waste isshredded tyre waste that includes at least integrally formed rubber andsteel mesh. Many prior reactors are unable to process shredded tyrewaste due to the presence of the steel mesh. However, this reactor isable to accommodate the steel mesh, and in some instances it isadvantageous to do so. Upon heating, the steel mesh provides an internalsource of heat that promotes the thermal degradation of rubber. Thesteel mesh also improves the turbulence and mixing of the rubber toimprove exposure to the heating environment and therefore improves thedegradation process and the quality of the char product.

As discussed above, the flighting on the screw auger tracks the internalcylindrical surface of the reactor in close relationship to minimise thetransport of material through the clearance space between outer edges ofthe flighting and the internal cylindrical surface of the reactor. Thisclose relationship (or tight tolerance) therefore mitigates materialshort-circuiting the system. The close relationship also prevents orlimits the transport of products from the thermal degradation reaction,including reaction gases, steel mesh, and carbon ash.

In one form, the clearance space between the outer edges of theflighting and the internal surface of the hermetically sealedcylindrical reactor is 7 mm or less. Preferably, the clearance space is6 mm or less. More preferably, the clearance space is 5 mm or less. Evenmore preferably, the clearance space is 4 mm or less. Most preferably,the clearance space is 3 mm or less. The inventors have found thathaving a tight tolerance between the flighting and the internal surfaceof the reactor advantageously minimises reactants and/or reactionproducts from inadvertently passing into or out of a thermal reactionzone, and short-circuiting the system or potentially having an adverseeffect on the reaction in subsequent zones.

In an embodiment, the reactor includes at least a first gas outlet and asecond gas outlet for withdrawing gas or gases evolved during thenon-oxidative thermal degradation of the rubber; wherein the first gasoutlet is located upstream of the second gas outlet, and the first gasoutlet is configured to withdraw the gas or gases at a larger volumetricflow rate than the second gas outlet. By upstream it is meant that thefirst gas outlet is located closer to the reactor inlet than the secondgas outlet.

In one or more forms of the above mentioned embodiment, the first gasoutlet and the second gas outlet are first and second gas extractionpipes, and the pressure drop across the second gas extraction pipe isgreater than the first gas extraction pipe. This difference in pressuredrop can be achieved in a number of different ways, for example: (i) thesecond gas extraction pipe has a smaller diameter than the first gasextraction pipe; (ii) the second gas extraction pipe is longer than thefirst gas extraction pipe; (iii) the second gas extraction pipe includesa flow restrictor; (iv) the second gas extraction pipe includes a valve,the valve being throttlable to increase the pressure drop through thesecond gas extraction pipe; or (v) a combination of one or more of theforegoing.

In a preferred arrangement, the first gas extraction pipe and the secondgas extraction pipe are connected to a common exhaust manifold, suchthat the gas or gases are withdrawn from the reactor via the first gasextraction pipe and the second gas extraction pipe, and are transportedto the common exhaust manifold. The exhaust manifold includes, or isconnected to, a gas extraction blower which applies a negative pressureto the exhaust manifold to withdraw the gas or gases through the firstgas extraction pipe and the second gas extraction pipe. As discussedabove, the pressure drop across the second gas extraction pipe isgreater than across the first gas extraction pipe, and as such thevolumetric flow rate of gas or gases extracted through the first outletgreater than that extracted through the second gas outlet.

It is preferred that the reactor includes at least a first thermalreaction zone upstream of a second thermal reaction zone; wherein thefirst gas outlet is arranged to withdraw gas or gases from the firstthermal reaction zone, and the second gas outlet is arranged to withdrawgas or gases from the second thermal reaction zone.

In still further forms of this embodiment, the reactor further includesa third gas outlet, wherein the third gas outlet is downstream of thesecond gas outlet. As above, the third gas outlet may be in the form ofa third gas extraction pipe. By downstream it is meant that third gasoutlet is located closer to the reactor outlet than the second gasoutlet. In this form of the invention, the first gas outlet isadditionally configured to withdraw the gas or gases at a largervolumetric flow rate than the third gas outlet. This may be achieved inthe same manner as generally described above. Alternatively, the secondand third outlets may be connected via a common gas extraction pipe. Ininstances where the second and third outlets are connected via thecommon gas extraction pipe, it is preferred that the common gasextraction pipe is of about the same length and diameter as the gasextraction pipe of the first outlet such that the volumetric gas flowrate through first outlet is about the same as the sum of the volumetricgas flow rate through the second and the third outlet. The third gasoutlet may be located either on a third thermal reaction zone (inembodiments that include at least three thermal reaction zones) or onthe outlet.

It will be appreciated that the reactor may include one more oradditional gas outlets that may exhibit the same pressure drop as thefirst gas outlet or a different pressure drop from the first gas outlet.The one or more additional outlets may be located up stream or downstream of any one of the first, the second, and the third outlets. Theone or more additional outlets may be associated with a reaction zonethat is different from the reaction zones associated with the first,second, and third outlets. An exemplary reactor includes a first, asecond, and a third reaction zone arranged sequentially from the inletof the reactor to the outlet of the reactor. This reactor furtherincludes an additional thermal reaction zone located between the firstand second reaction zones. The first thermal reaction zone includes afirst gas outlet with first gas extraction pipe, the second thermalreaction zone includes a second gas outlet with second gas extractionpipe, the third thermal reaction zone includes a third gas outlet withthird gas extraction pipe, and the additional thermal reaction zoneincludes an additional gas outlet in the form of a corresponding gasextraction pipe. In this example, the second and third gas extractionpipes are connected via a T- or Y-junction that then connects to anexhaust manifold that is additionally connected to the first gasextraction pipe and the gas extraction pipe of the additional gasoutlet. Each of the gas extraction pipes may be of the same size orlength such that the pressure drop between each outlet and the exhaustmanifold is about the same. However, as the second and third gas outletsare connected via the T- or Y-junction upstream of the manifold, thevolumetric flow rate of gas through each of the second and third outletsis effectively half the volumetric flow rate of gas through the firstoutlet and the additional outlet.

The reactor may include a plurality of thermal reaction zones, such asfrom two to five thermal reaction zones e.g. two, three, four, or fivereaction zones (although more are possible). In one such embodiment, thereactor includes:

at least two thermal reaction zones including:

-   -   a first thermal reaction zone including one or more first        heating elements, the one or more first heating elements        controllable to heat the first thermal reaction zone to a first        operating temperature, and    -   a second thermal reaction zone including one or more second        heating elements, the one or more second heating elements        controllable to heat the second thermal reaction zone to a        second operating temperature different to the first operating        temperature.

In one form of this embodiment, the reactor includes at least threethermal reaction zones, and additionally includes a third thermalreaction zone including one or more third heating elements, the one ormore third heating elements controllable to heat the third thermalreaction zone to a third operating temperature different to the firstand/or second operating temperature.

In still another form of this embodiment, the reactor includes at leastfour thermal reaction zones, and additionally includes a fourth thermalreaction zone including one or more fourth heating elements, the one ormore fourth heating elements controllable to heat the fourth thermalreaction zone to a fourth operating temperature different to the firstand/or second and/or third operating temperature.

In various forms of the above embodiments and as appropriate, the firstthermal reaction zone includes a first gas outlet, the second thermalreaction zone includes a second gas outlet, the third thermal reactionzone includes a third gas outlet, and the fourth thermal reaction zoneincludes a fourth gas outlet. Each gas outlet for withdrawing gas orgases evolved during the non-oxidative thermal degradation of the rubberin the corresponding zone. In a preferred form, the pressure drop acrossthe first gas outlet is lower than the pressure drop against one or moreof the second and/or third and/or fourth gas outlet.

In one form the reactor includes a heating zone configured to receivethe tyre waste from the inlet and pre-heat the rubber containing waste,wherein the heating zone does not include a gas outlet. The purpose ofthe heating zone is to heat the rubber containing waste to soften therubber. Generally gases are not evolved in this process, and as such,the heating zone does not include a gas outlet.

In one form, the inlet to the reactor includes an inlet air lock chamberand/or the outlet from the reactor includes an outlet air lock chamber.The use of these airlocks prevents or minimises the ingress of oxygen.This is important for providing a reaction environment that isfavourable to the thermal degradation of rubber in the rubber containingwaste. Preferably, the inlet air lock chamber is formed between twoknife gate valves. The use of knife gate valves (instead of other valvetypes) has been found to provide an effective barrier against the entryof air into the respective airlock chambers. Alternatively, oradditionally, the outlet air lock chamber is formed between two orificeknife gate valves. The use of orifice knife gate valves is particularlyadvantageous as carbon ash (as well as any oil that has condensed withthe carbon ash) has a tendency to form a gunk in the moving componentsof standard gate and rotary valves.

In one form, the rate and direction of the screw auger is controllable.This advantageously allows the residence in the reactor to becontrolled. Additionally, the ability for the auger to rotate in boththe forward and backward direction additionally provides for an extendedresidence time while agitating the rubber containing waste material. Asresidence time can be increased in this manner, the length of thereactor can be reduced. Preferably the residence time of the rubbercontaining waste in the reactor is less than 2 hours, more preferably1.5 hours or less, and even more preferably 1 hour or less.

In one form, the reactor is sized to fit within a standard sizedshipping container of dimensions 40 ft long×8 ft wide×8 ft 6 in high.This is useful as it allows the reactor to be easily prepared fortransport and shipping. It also allows provides a modular system forwhich the capacity can be easily expanded by adding further processmodules including additional reactors.

There is further disclosed herein a system for non-oxidative thermaldegradation of rubber containing waste into a char product, the systemincluding:

-   -   the reactor described above, and    -   a control system configured to:        -   heat each thermal reaction zone to the operating            temperature, and        -   communicate with a gas extraction system to maintain each            thermal reaction zone at an negative operating pressure.

In one form, the control system is further configured to control therate of rotation of the auger, and to operate the screw auger in boththe forward and reverse directions.

In one form, the system further including ancillary processing equipmentincluding:

-   -   a feed conveyor for transporting tyre waste to the inlet;    -   the gas extraction system including:        -   at least a condenser for condensing a condensable portion of            the gas or gases into a liquid product, and    -   a product conveyer for transporting the char product to a        separator, and    -   the separator for separating the char product into a metal        containing fraction and a carbon char fraction.

In one form of the above embodiment, the gas extraction systemadditionally includes a burner and flue gas stack for combusting anon-condensable portion of the gas or gases and dispersing resultingflue gas or gases. In another form of the invention, the gas extractionsystem includes a gas fired generator to generate electricity viacombustion of the non-condensable portion of the gas or gases. Thiselectricity may be used to power at least a portion of the system.

In one form, the ancillary equipment further includes: a mill tocomminute the carbon char fraction, and a cooling tower for coolingprocess water.

In one form, the ancillary equipment is compactible to fit within astandard sized shipping container of dimensions 40 ft long×8 ft wide×8ft 6 in high.

In a first aspect of the invention, there is provided a process for thenon-oxidative thermal degradation of a rubber containing wasteincluding:

transporting the rubber containing waste along a horizontal axis of ahermetically sealed cylindrical reactor including:

an inlet and an outlet,

one or more thermal reaction zones arranged between the inlet and theoutlet, wherein each thermal reaction zone is provided with:

-   -   one or more heating elements controllable to heat the thermal        reaction zone to an operating temperature for mediating the        non-oxidative thermal degradation of rubber in the rubber        containing waste, and    -   one or more gas outlets for withdrawing volatile gas or gases        evolved during the non-oxidative thermal degradation of the        rubber; and

a screw auger located within the reactor, the screw augur configured torotate in both the forward and reverse directions to agitate andtransport the rubber containing waste through the one or more thermalreaction zones in both the forward and reverse directions and to theoutlet,

subjecting the rubber containing waste, in the one or more thermaltreatment zones, to a temperature above the degradation temperature ofrubber for a time sufficient to produce the volatile gas or gases andthe char product;

operating the screw auger in both the forward and reverse directions toagitate the rubber containing waste within the reactor; and

advancing the rubber containing waste along the horizontal axis to theoutlet.

In a second aspect of the invention there is provided a process for thenon-oxidative thermal degradation of rubber containing waste including:

feeding the rubber containing waste through an inlet and into ahermetically sealed cylindrical flow-through reactor having one or morethermal treatment zones arranged along a horizontal axis of the reactorbetween the inlet and the outlet of the reactor,

wherein each thermal reaction zone is provided with:

-   -   one or more heating elements controllable to heat the thermal        reaction zone to an operating temperature for mediating the        non-oxidative thermal degradation of rubber in the rubber        containing waste, and    -   one or more gas outlets for withdrawing gas or gases evolved        during the non-oxidative thermal degradation of the rubber;

operating one or more thermal treatment zones at a temperature at orabove the thermal degradation temperature of rubber;

operating a screw auger in both the forward and reverse directions toagitate the rubber containing waste within the reactor and to transportthe rubber containing waste along the horizontal axis of the reactor,and through the reactor at a rate to provide a residence time in the oneor more thermal treatment zones sufficient to heat the rubber containingwaste to a temperature above the degradation temperature of rubber, andto degrade rubber in the rubber containing waste into a volatile gas orgases and a char product;

applying a negative pressure to each thermal treatment zone to withdrawvolatile gas or gasses that are formed in that thermal treatment zonefrom the non-oxidative thermal degradation of the rubber; and

discharging the char product through an outlet of the reactor.

In an embodiment of the first and/or second aspects, the volatile gas orgases include limonene.

In an embodiment of the first and/or second aspects, flighting on thescrew auger tracks the internal cylindrical surface of the reactor inclose relationship to minimise or prevent the transport of the volatilegas or gasses and/or the char product through a clearance space betweenouter edges of the flighting and the internal cylindrical surface of thereactor.

In an embodiment of the first and/or second aspects, the reactorincludes:

at least two thermal reaction zones including:

-   -   a first thermal reaction zone including one or more first        heating elements, the one or more first heating elements        controllable to heat the first thermal reaction zone to a first        operating temperature, and    -   a second thermal reaction zone including one or more second        heating elements, the one or more second heating elements        controllable to heat the second thermal reaction zone to a        second operating temperature different to the first operating        temperature;

the process further including:

-   -   operating the first thermal reaction zone at the first operating        temperature, the first operating temperature sufficient to form        a first volatile gas or gases, and    -   operating the second thermal reaction zone at the second        operating temperature, the second operating temperature being        higher than the first operating temperature, to enhance the        conversion of the rubber to the char product and from a second        volatile gas or gases.

It will be appreciated that the reactor may additionally include one ormore further thermal reaction zones which may be located upstream and/ordownstream of the first and/or second thermal reaction zones, each ofthe further reaction zones including corresponding heating elementsand/or corresponding gas outlets for withdrawing gas or gases evolved inthat thermal reaction zone.

It is preferred that in the first thermal reaction zone is operated at atemperature of from about 445° C. to about 550° C. More preferably, 450°C. and up to 530° C., and most preferably from 460° C. and up to 500° C.Additionally, or alternatively, it is preferred that the second thermalreaction zone is operated at a temperature of at least 550° C. Morepreferably, the second thermal reaction zone is operated at atemperature of below 1370° C. Even more preferably, up to 700° C. Stillmore preferably, up to 650° C.

It is preferred that the process further includes heating the rubbercontaining waste in the first thermal reaction zone to a temperature offrom about 445° C. to about 550° C. More preferably, 450° C. and up to530° C., and most preferably from 460° C. and up to 500° C.Alternatively, or additionally, it is preferred that the processincludes heating the rubber containing waste in the second thermalreaction zone to a temperature of at least 550° C. More preferably, upto 1370° C. Even more preferably, up to 700° C. Still more preferably,up to 650° C.

It is preferred that the first volatile gas or gases is a sulfur gas orsulfur containing gas.

It is preferred that the second volatile gas or gases is substantiallyfree of sulfur.

It is preferred that the second volatile gas or gases include limonene.

It is preferred that, the process further includes: applying a firstnegative pressure to the first thermal reaction zone, and applying asecond negative pressure to the second thermal reaction zone. It ispreferred that the first negative pressure and the second negativepressure are different. Typically the negative pressure applied to eachof the thermal reaction zones is about −0.1 kPa. However, in anembodiment, a negative pressure of about −0.05 kPa is applied to theoutlet. Preferably, a first gas is withdrawn from the first thermalreaction zone at a first gas volumetric flow rate, and a second gas iswithdrawn from the second thermal reaction zone at a second gasvolumetric flow rate, and wherein the first gas volumetric flow rate isgreater than the second gas volumetric flow rate. Preferably, the firstgas volumetric flow rate is from 1.1 to 3 times the second gasvolumetric flow rate. More preferably the first gas volumetric flow rateis from 1.2 to 2.8 times the second gas volumetric flow rate. Still morepreferably the first gas volumetric flow rate is from 1.3 to 2.6 timesthe second gas volumetric flow rate. Even more preferably the first gasvolumetric flow rate is from 1.4 to 2.4 times the second gas volumetricflow rate. Most preferably the first gas volumetric flow rate is from1.5 to 2.2 times the second gas volumetric flow rate.

In an embodiment of the first and/or second aspects, the process furtherincludes the step of pre-heating the rubber containing waste to atemperature of at least 300° C. prior to transporting the rubbercontaining waste through the one or more thermal reaction zones.Preferably, the step of pre-heating the rubber containing waste isconducted in a heating zone of the reactor located upstream of the oneor more thermal reaction zones.

In an embodiment of the first and/or second aspects, the process furtherincludes the step of cooling the char product to a temperature of noless than about 400° C. prior to discharging the char product from thereactor. Preferably, the step of cooling the rubber containing waste isconducted in a cooling zone of the reactor located downstream of the oneor more thermal reaction zones. In this context, the term “cooling zone”is intended to refer to a zone which is operated at a lower temperaturethan the thermal reaction zones, wherein the temperature of the charproduct is reduced. However, in the cooling zone, the char product ismaintained at a temperature of no less than about 400° C., and as such,the cooling zone may be provided with one or more heating elements tomaintain the desired temperature and/or one or more gas outlets.

In an embodiment of the first and/or second aspects, the process furtherincludes feeding the rubber containing waste through the inlet via aninlet air lock chamber located upstream of the inlet to prevent orminimise the ingress of oxygen through the inlet and into the reactor.The rubber containing waste may be pre-heated in the air lock chamber.

In an embodiment of the first and/or second aspects, the process furtherincludes discharging the char product from the outlet and into an outletair lock chamber to prevent or minimise the ingress of oxygen throughthe outlet and into the reactor.

In an embodiment of the first and/or second aspects, the step oftransporting the rubber waste along the horizontal axis of the reactorincludes transporting the waste along an axial reactor length that isless than about 40 ft.

In an embodiment of the first and/or second aspects, the processincludes operating the screw auger in both the forward and reversedirections to agitate the rubber containing waste within the reactor.

In an embodiment of the first and/or second aspects, the rubbercontaining waste is shredded tyre waste that includes at least rubber,steel, and nylon, and the process includes transporting the shreddedtyre waste along the horizontal axis of the hermetically sealedcylindrical reactor. In such cases, it is preferred that afterdischarging the char product from the reactor, the process includesseparating the char product into a metal containing fraction and acarbon char fraction.

In an embodiment of the first and/or second aspects: condensing acondensable fraction of the volatile gas or gases into a liquidcondensate.

In an embodiment of the first and/or second aspects, the non-oxidativethermal degradation of the rubber is carried out in the absence of anamount of a catalyst that substantially affects the rate of degradationof the rubber. It is preferred that the non-oxidative thermaldegradation of the rubber is carried out in the absence of a catalyst.

In another aspect of the invention, there is provided a methodincluding: using the hermetically sealed flow-through reactor or systemdescribed herein for the thermal degradation of a rubber containingwaste.

In still another aspect of the invention, there is provided the use ofthe hermetically sealed flow-through reactor or system described hereinfor the thermal degradation of a rubber containing waste.

In still a further aspect of the invention, there is provided thehermetically sealed flow-through reactor or system as described hereinwhen used to thermally degrade a rubber containing waste.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising”, “comprises”and “comprised”, are not intended to exclude further additives,components, integers or steps.

Further aspects of the present invention and further embodiments of theaspects described in the preceding paragraphs will become apparent fromthe following description, given by way of example and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram showing the primary unit process forthe thermal degradation of rubber containing waste.

FIG. 2 is an elevation schematic of an embodiment of the reactor for thethermal degradation of the rubber containing waste.

FIG. 3 is a plan schematic of the embodiment of the reactor of FIG. 2.

FIG. 4 is a cross section along the axis of the reactor of FIG. 2.

FIG. 5 is a cross section orthogonal to the axis of the reactor of FIG.2.

FIG. 6 is a schematic of an embodiment of the reactor showing thelocation of temperature sensors.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A schematic of the system 100 for thermal degradation (also known asdepolymerisation) of rubber containing waste is shown in FIG. 1. Thisschematic is illustrative of an embodiment of the system 100, and shouldnot be construed in a limiting manner. The skilled addressee willappreciate that the system 100 may include other unit processes, as wellas sensors and controllers (which are not illustrated).

The system 100 can be used to process a wide variety of different rubbercontaining wastes, but is particularly adapted for a feedstock of tyrewaste 102. The tyre waste 102 will generally be in the form of shreddedor stripped tyre waste. Shredded tyres are tyres that have been runthrough a shredder without any separation of the different tyrecomponents (such as rubber and steel mesh). As such, shredded wasteconsists of size reduced pieces of tyre that retain at least rubber,steel mesh, and other reinforcement fibres in an integrated form. Thisis in comparison to stripped rubber tyre waste that consists primarilyof tread rubber that has been stripped from the body of the tyre.Stripped rubber tyre waste does not include steel mesh. The system ispreferably used to treat shredded tyre waste, such as 100 mm or 50 mmclassified shredded tyre waste.

The system 100 and process makes use of a hermetically sealedcylindrical flow through reactor 112. The reactor has a cylindricalreactor body, such as in the form of a sheet metal or plate metal shell,and the cylindrical reactor body has an internal cylindrical surface andan external cylindrical surface. The advantages of the external andinternal cylindrical surfaces are discussed in relation to certainembodiments below.

The tyre waste 102 is fed via a conveyor 104 into an airlock chamber 106between inlet valve 108 and outlet valve 110. During loading of theairlock chamber 106, inlet valve 108 is in the open position to permitpassage of the tyre waste there through while outlet valve 110 is in theclosed position. Once the air lock chamber 106 has been loaded with tyrewaste, inlet valve 108 is moved to the closed position providing ahermetic seal to airlock chamber 108. Outlet valve 110 can then beopened to permit passage of the tyre waste from the airlock chamber 108into a hermetically sealed flow-through reactor 112. The reactor 112 isoriented horizontally, such that the reactor 112 has a horizontal axisalong which the tyre waste is transported through the reactor 112. Thearrangement of airlock chamber 106 with valves 108 and 110 is to limitor minimise the introduction of air (in particular oxygen) into thereactor 112. It will be appreciated that a range of different airlockarrangements may be used. For example, a wide variety of differentvalves may be used as valves 108 and 112. By way of example, rotaryvalves are commonly used in airlock arrangements, and may be employed inthis situation. However, the inventors have found that the use ofknife-gate valves is preferable. In addition to providing an effectivegas seal, knife-gate valves are of simpler design, less prone toblockage, more tolerant of different feed sizes and types, and aregenerally of smaller size than rotary valves which allows the system tobe more compact. It will be appreciated that some air (including oxygen)will be entrained with the tyre waste as it is introduced and sealed inairlock chamber 106.

An embodiment of the reactor 112 is illustrated in FIG. 2 In theembodiment of FIG. 1, the reactor 112 is divided into four differentthermal zones: a heating zone 112A, a first thermal reaction zone 112B,a second thermal reaction zone 112C, and a cooling zone 112D. Each ofthese thermal zones is provided with a heater 114A, 114B, 114C, and 114Drespectively. The size and number of thermal zones provided in a givenreactor is dependent on the chemical make-up and nature of the wastefeedstock. However, generally it is desirable to have at least a heatingzone, a cooling zone, and at least one thermal reaction zone therebetween. The present embodiment includes two thermal reaction zones, thereasons for which will be discussed in more detail later. It should alsobe noted that the size of each of the thermal zones may be the same ordifferent. The size of each thermal zone depends on the desiredresidence time in that zone. By way of example, heating and coolingprocesses may require less residence time to achieve completion thanrubber depolymerisation in the thermal reaction zones 112B and 112C. Insuch instances, the thermal reaction zones 112B and 112C will bedimensionally longer than the heating and cooling zones 112A and 112Drespectively. Further, the thermal reactions occurring in thermalreaction zones 112B and 112C may require different residence times, inwhich case thermal reaction zones 112B and 112C are of differentlengths. It will be appreciated that in some embodiments, the heatingzone 112A and the cooling zone 112D may be separate thermal reactionzones or may form a part of the same thermal reaction zone.

Each of the zones 112A, 112B, 112C, and 112D is illustrated as havingonly a single heater. However, it will be appreciated that each of thesezones may have plural heaters. Plural heaters may be used to ensure thata more consistent temperature is maintained across the full length of azone, or to apply a temperature gradient across a zone. The number ofheaters per thermal zone may differ depending on the size and/or heatrequirements of that zone. The skilled addressee will appreciate that arange of different heaters may be used for example: electric heaters,induction heaters, or a combination thereof (although it should be notedthat induction heaters are only suitable when the tyre waste includes aferromagnetic material such as steel or iron—e.g. shredded tyre waste).The inventors have found that electric band heaters are particularlyuseful with the cylindrical reactor design as they allow for the reactorto process a wide variety of different rubber wastes. Band heaters canalso be used to as well as providing a reasonably consistent andcontrollable temperature profile in along the axial direction of athermal zone, and a controllable temperature gradient in the radialdirection. Each of the heaters in a given zone may be controlledindependently of any other heater in that zone. For example, where athermal reaction zone includes a plurality of band heaters, each ofthose heaters may be independently controllable to ensure a desiredtemperature or temperature gradient is maintained across that zone. Suchcontrol may be desirable where two adjacent zones are operated atsignificantly different temperatures.

The tyre waste is received from the airlock 106 into the heating zone112A of the reactor 112. It will be appreciated that some air (and hencesome oxygen) is entrained with the tyre waste when it is fed into theairlock 106, and as such, this air will be fed into the reactor 112along with the tyre waste. However, the amount of air entrained with thetyre waste is small, and the airlock 106 effectively prevents extraneousair from flowing into the reactor.

In this the heating zone 112A, the tyre waste is pre-heated to atemperature that is below the thermal degradation temperature of rubberin order to soften the rubber in the tyre waste. The purpose of theheating zone 112A is to provide sufficient heat energy to overcome theenergy absorbance of the rubber itself while maintaining a safetemperature which avoids potential explosion as a result of the exposureof any volatile gases formed in the heating zone 112A to oxygen gasentrained in the tyre waste feed. The tyre waste is typically heated toa temperature in the range of 200° C. to 400 350° C., preferably 250° C.to 350 330° C., more preferably 280° C. to 320° C., and most preferablyabout 300° C. The thermal degradation of rubber commences fromapproximately 320° C., as such, it is generally preferred that thetemperature does not substantially exceed this value. However, it may bebeneficial in some instances to heat the tyre waste to a temperatureslightly above that required for degradation so that rubber degradationhas commenced as the tyre waste is fed into the first thermal reactionzone. Once the tyre waste has reached the desired temperature, the tyrewaste is fed into the thermal reaction zones for processing. In thepresent embodiment, the tyre waste is first processed in thermalreaction zone 112B prior to further processing in thermal reaction zone112C. In some embodiments, the heating zone is a sub-portion of thefirst thermal zone.

In the first thermal reaction zone 112B, the tyre waste is heated andprocessed at a temperature sufficient to break sulfur bonds invulcanised rubber, and to volatilise sulfur and/or sulfur compounds inthe rubber. Preferably, the temperature of the first thermal reactionzone (and thus the temperature to which the tyre waste is heated) isabove the boiling point of sulfur (444.6° C.) but below the temperatureat which complete depolymerisation of rubber molecules occurs. In viewof this, it is preferred that the first thermal reaction zone 112B isoperated at a temperature of from at least 445° C. and up to 550° C.More preferably, the first thermal reaction zone 112B is operated at atemperature of from 450° C. and up to 530° C., and most preferably from460° C. and up to 500° C. By “operated at a temperature” it is meantthat the tyre waste in that zone is heated to a temperature within thespecified range. Reaction gases including the volatilised sulfur and/orsulfur compounds are extracted from the system via gas extraction pipe116 and sent to a condenser 118 via exhaust manifold 120 and gasextraction blower 122 where any condensable fraction is separated andstored in storage tank 124 and any non-condensable fractions are flaredin burner 126. To this end, the gas extraction blower is operated toapply a suction pressure (or negative pressure) to the reactor 112.Primarily, the gas generated in the first reaction zone is anon-condensible gas that includes gaseous sulfur and/or sulfurcompounds, which when flared form sulfur oxides (SOx). However, somedepolymerisation of rubber into volatile organic compounds (VOC) mayoccur, and these VOCs can be separated as a condensable fraction. As aresult of treatment in the first thermal reaction zone 112B a reducedsulfur tyre waste is formed. This reduced sulfur tyre waste is thenpassed into the second thermal reaction zone 112C.

In the second thermal reaction zone 112C, the reduced sulfur tyre wasteis heated above the temperature required for the complete thermaldegradation of rubber. This results in depolymerisation of rubber in thetyre waste into VOCs and carbonaceous ash (primarily carbon butgenerally also contains other non-organic ash components). The type ofVOCs that are formed is dependent, in part, on the temperature of thiszone. At higher temperatures depolymerisation products from thedegradation of rubber may themselves further degrade into smaller VOCs.By way of example, the formation of smaller VOCs suitable for use as afuel (such as diesel) generally require high temperatures of 1400° C. orgreater. In view of this, the temperature of this zone 112C may beselected to target the production of particular VOCs. Generally, thesecond reaction zone is operated at a temperature of at least 550° C.However, higher temperatures may be advantageous as they provide a morerapid rate of thermal degradation, but this needs to be balanced againstincreased cost from higher energy usage and the desired output VOCs. Theupper temperature limit in this zone 112C will ideally be below 1370° C.(such as 1350° C. or 1300° C.). As above this temperature, any steel inthe tyre waste will melt. Molten steel may damage the reactor and createdownstream problems, such as with the separation of the char residueinto a metal containing portion and a non-metal containing portion.Notwithstanding the above, it is generally desirable that the uppertemperature limit of this zone is 700° C. At temperatures above 700° C.the fibres (originally present in the sidewall portion of the tyres)begin to break down. The degradation of these fibres may producechlorine which can react with rubber depolymerisation products to formchlorinated furans (such as polychlorinated dibenzofurans). Chlorinatedfurans are hazardous to the environment and human health, and as suchthe production of these compounds is undesirable. Even more preferablythe upper temperature limit of this zone is 650° C., and most preferably600° C. A preferred operating temperature is in the range of 550° C. to600° C. which favours the production of dl-limonene. The limonene may bein the form of d-limonene, l-limonene, or dl-limonene.

The VOCs formed in the second thermal reaction zone 112C are removed viaextraction pipe 128, exhaust manifold 120 and gas extraction blower 122,before being processed in condenser 128 where the condensable organiccompounds are separated from any non-condensable components and storedin storage tank 124. The non-condensable components are flared in burner126. By the end of this stage, the solid residue that remains is in theform of char residue (e.g. primarily a fine particulate carbonaceous ashand steel mesh). This char residue is then passed to the cooling zone112D.

The cooling zone is typically operated at a temperature sufficient toprevent condensation of any VOCs that have not been extracted into aliquid (such as fuel oil) and thus produces a dry char residue product.Typically the cooling zone will be operated at a temperature of fromabout 400° C. to about 500° C. In this case, the cooling zone is alsoprovided with gas extraction pipe 130 (which connects to manifold 120)to further remove volatile organics as a result of the degradationprocess. After the cooling zone, the tyre residue is discharged throughan outlet.

The tyre waste is transported from the inlet, through the heating zone112A, the first thermal reaction zone 112B, the second thermal reactionzone 112C, and then the cooling zone 112D by an auger 131. The auger 131includes flights which tracks the internal cylindrical surface of thereactor in close relationship. This arrangement has a number ofadvantages over systems that employ a typical screw conveyer system inwhich the auger is located within a standard commercially availableU-shaped channel. By way of example, such a system is described inAustralian patent publication 2013100048 A4 (“AU 2013100048”).

AU 2013100048 describes a reactor that includes a U-shaped reactor basedon a modified standard U-shaped screw conveyer system. In this case, theU-shaped screw conveyer has been modified to include a removable topsection which acts to close the open ends of the “U” while providingeasy access to the main reactor chamber if required. Thus the reactor ofAU 2013100048 does not have an internal cylindrical surface, and theauger of AU 2013100048 is unable to track the internal surface in closerelationship.

The arrangement of the present invention provides a number of advantagesover the U-shaped reactor design of AU 2013100048. In particular, theU-shaped reactor design of AU 2013100048, by virtue of its shape,provides substantial clearance between the rotational conveyancingmechanism and the upper internal surface of the removable top section.The inventors discovered that this allowed rubber clumps to bouncethrough the rotational conveyancing mechanism from the inlet to theoutlet without receiving adequate pyrolytic treatment. In effect, these“bouncers” short-circuited the system resulting in an ash product thatundesirably included an amount of un-treated or partially treatedrubber. Another issue with the U-shaped reactor design of AU 2013100048that the inventors have discovered is that the aforementioned clearancepermits gases evolved from the pyrolytic degradation of rubber totransfer between different thermal zones of the reactor. This isundesirable as the presence of gases evolved in one thermal zone canhave an adverse effect on the thermal degradation of rubber andassociated production of gases in another thermal zone. Furthermore, anyoxygen that is introduced into this U-shaped reactor is also able toshort circuit the system. This is highly dangerous as this permits theoxygen to mix with the volatile gases in a high temperatureenvironment—which can lead to an explosion.

As a further point of difference, AU 2013100048 discloses a methodand/or system that includes a magnetic separation process and a clothseparation process upstream of the U-shaped reactor. Thus, any steel orcloth (such as nylon) is removed prior to the thermal degradationprocess. This allows the process of AU 2013100048 to be operated at hightemperatures, such as in excess of 1400° C. There are two keymotivations to operate at these high temperatures, the first is toincrease the rate of rubber degradation, and the second is to target theproduction of VOCs that can be used as a fuel for a generator to offsetthe process energy requirements. In contrast, the present invention usesa lower degradation temperature than is typical with rubber degradationprocesses. This is due to the presence of steel and nylon or fibres inthe tyre waste and the desire to avoid depolymerisation of the fibres,but also to favour the production of limonene. Depolymerisation of tyrerubber into limonene generally occurs at temperatures below 700° C.Limonene will be broken down into smaller molecules at the standardtemperatures used for rubber pyrolysis.

In view of the above, AU 2013100048 provides no motivation or teachingto operate the U-shaped reactor at a temperature that is significantlylower than standard rubber degradation processes. AU 2013100048discloses operating temperatures in excess of 1400° C. which isconsistent with the upstream metal and cloth removal processes, and thedesire in AU 2013100048 to form volatile gases that can be combusted ina generator to provide electricity.

To address the above discussed shortcomings, the inventors developed anew cylindrical reactor in combination with an auger having flightssized such that there is a tight tolerance between the flights and theinternal in cylindrical walls of the reactor. This tight tolerancemitigates or prevents both the occurrence of “bouncers” as well astransfer of gases in the clearance space between edges of the flightingand the internal walls of the reactor. As a result of this arrangement,substantially all of the volatile gases evolved in a thermal reactionzone are transported along with the degrading rubber waste in a channelformed between successive flights of the auger. This arrangement, alsohelps to prevent any entrained oxygen gas from short circuiting throughthe system, and thus substantially reduces the risk of explosion.

After passing through the reactor 112, the char product is fed into anair lock chamber 132 between inlet valve 134 and outlet valve 136. Thisairlock chamber 132 operates in much the same manner as airlock chamber106 to prevent or minimise the ingress of air into reactor 112. Briefly,inlet valve 134 and outlet valve 136 are generally in the closedposition. As the char product is discharged from the reactor 112, inletvalve 134 is opened so that the char product can be received into theairlock chamber 132. Once airlock chamber 132 is loaded, inlet valve 134is closed. Outlet valve 136 then opens so that the char product can betransferred to conveyor 138, after which outlet valve 136 is thenclosed. A wide variety of different valves may be used as valves 134 and136. By way of example, rotary valves and gate valves may be employed.It is preferred that orifice plate knife gate valves are used. Theinventors found that the particulate ash in the char residue tended toinfiltrate and form a gunk in the moving components of standard gate androtary valves. The use of an orifice plate knife gate valves mitigatesthis.

Conveyor 138 transports the char product to a separator 140. Duringtransport on conveyor 138, the char product continues to cool. Theseparator 140 separates the char product into a metal containingfraction 142 that includes the steel mesh, and a non-metal containingfraction 144 that is the particulate carbonaceous ash. A variety ofdifferent separation processes may be used, for example a simple screenmay be employed which permits the passage of the particulatecarbonaceous ash therethrough, while diverting the steel mesh into aseparate stream. Alternatively, a magnetic separator may be employed.

The system 100 is controlled by a control system (not illustrated). Thecontrol system is used to control the temperature, negative pressure,and residence time within each of the thermal zones 112A, 112B, 112C,and 112D of the reactor 112. The control system may include sensors forreporting parameters back to the control system. These sensors may belocated to determine the temperature and/or pressure in each of thethermal zones 112A, 112B, 112C, and 112D of the reactor 112; and/orrotational speed of the auger 131.

Temperature can be controlled in each zone by controlling each of theheaters 114A, 114B, 114C, and 114D.

Negative pressure can be controlled in the reactor 112 through controlof the gas extraction blower 122, through throttling valves (not shown)upstream of the gas extraction blower 122 such as on lines 116, 128,130, or in manifold 120; or valves (also not shown) that are downstreamof the gas extraction blower 122. As discussed previously, the size andarrangement of the auger 131 within the reactor 112 minimises gascommunication between thermal zones 112A, 112B, 112C, and 112D, as such,in some embodiments the control system is also able to apply a differentnegative pressure across a particular zone and/or apply or vary pressuredrop across each of lines 116, 128, or 130, such as by including a flowrestrictor or a throttlable valve on one or more of lines 116, 128, or130 (if present). Alternatively, application of different negativepressures to each of the thermal reaction zones may be affected byhaving a different pressure drop across lines 116, 128, or 130, whichmay be achieved by having lines of different size and/or shape, or themanner in which lines 116, 128, and 130 are connected to manifold 120.Applying different negative pressures to different zones is particularlybeneficial where different gaseous reaction products (or differentamounts of those products) are produced in the different zones, such aswith the present system where sulfur based gases are evolved in thermalreaction zone 112B and hydrocarbon based gases are evolved in thermalreaction zone 112C. Maintaining differently pressured environments canalso be used to favour production of certain organic compounds overothers. For example, a first thermal reaction zone may be operated at afirst pressure, and a second thermal reaction zone may be operated at asecond pressure, wherein the first pressure and the second pressure aredifferent. In each case, the pressure is a function of the temperature,the quantity of volatile gases, and the application of negative pressureapplied via the gas extraction pipe for that thermal reaction zone.

Residence time in the reactor 112 can be controlled by altering thespeed and/or direction of rotation of the auger 131. Slower rotationalspeeds result in a longer residence time, whereas fast rotational speedsresult in short residence times. The inventors have also found that thelength of the reactor 112 can be reduced by adopting an operatingstrategy whereby the auger 131 moves in both the forward and thebackward direction. This forward-backward movement is also beneficialfor agitating the tyre waste as it moves through the system. By way ofexample, one such operating strategy is for the auger 131 to rotateforward (F) a set distance (or for a set time), then rotate backward (B)for the same distance and time, and then forward again before repeatingi.e. F-B-F, F-B-F etc. The skilled addressee will appreciate thatdifferent operating patterns may be used and is not limited to a 3 stepF-B-F pattern. The skilled addressee will also appreciate that each ofthe F and B steps may be the same or different in terms of duration,speed, or number of auger rotations, provided that the tyre waste isultimately progressed from the inlet to the outlet of the reactor 112.

In addition to providing control of the process, the controller mayadditionally be programmed so that it can determine appropriateoperating conditions for different feedstock. The operating conditionsmay change based on the size of the feed (for example, 50 mm shred tyrewaste will typically require less processing time than 100 mm shred tyrewaste), the desired output products (for example, depolymerisation ofrubber into smaller organic molecules generally requires a higheroperating temperature), or the nature of the material to be treated(such as the type of rubber, the presence of other constituents with therubber such as fibre or steel mesh) etc.

In various embodiments, the control system is also configured to controlthe other unit processes to ensure that operation of the overall processis streamlined. Thus, the control system may be configured to control:conveyors 104 and 132; the loading and unloading of airlock chambers 106and 12 via valves 108, 110, 134, and 136 respectively; separator 140;condenser 118; and operation of burner 126.

Another embodiment of a cylindrical reactor 212 of the invention isillustrated in FIGS. 2 and 3. In this embodiment, the cylindricalreactor 212 is formed from steel plate and has an internal cylindricalsurface and an external cylindrical surface.

The reactor 212 includes: an inlet air lock chamber 206 located betweenknife gate valves 208 and 210, an outlet air lock chamber 232 locatedbetween orifice plate knife gate valves 234 and 236, and a cylindricalbody (generally shown as 212) located there between. In use, rubbercontaining waste is fed into the reactor from inlet airlock chamber 206and through valve 210. The rubber containing waste is then transportedalong the horizontal axis of the cylindrical reaction 212 where it isconverted into the char product which is then discharged via valve 234into outlet airlock chamber 232. Once the outlet airlock chamber 232 isfull, valve 234 closes and valve 236 is subsequently opened to releasethe char product from the outlet airlock chamber 232.

The rubber containing material is transported along the horizontal axisof the reactor 212 via a screw auger 231 that is located within thereactor 212. Each of FIGS. 2 and 3 show the motor component of the screwauger 231 projecting from the inlet end of the reactor 212. This motorcan be controlled to rotate the screw auger 231 in both the forward andreverse directions as generally described in relation to the embodimentof FIG. 1.

In this embodiment, the reactor 212 includes twenty eight band heaters(generally labelled as 214) which are located at various intervals alongthe horizontal axis and on the external surface of the reactor 212. Thisarrangement of band heaters 214, in combination with the cylindricalgeometry of the reactor 212 provides for even heat transfer into thereactor 212 in at least the radial direction. The axial spacing of theband heaters may be selected so as to effectively maintain asubstantially constant temperature profile across a given reaction zone.

In this particular embodiment, the reactor includes four reaction zonesspaced along the horizontal axis labelled 254A, 254B, 254C, and 254D.Each of the thermal reaction zones 254A to 254D includes a plurality ofband heaters and a gas outlet (see 216, 228, 230A and 230B). In order toeffectively control the temperature in each thermal reaction zone 254A,254B, 254C, and 254D, a plurality of temperature sensors 252A to 252Lare spaced along the horizontal axis of the reactor 212. Each thermalreaction zone 254A, 254B, 254C, and 254D also includes a correspondinggas outlet 216, 228, 230A and 230B. A negative pressure is applied viaeach gas outlet 216, 228, 230A and 230B to withdraw volatile gases thatare formed in the corresponding zone. Pressure sensors 250A to 250D arelocated in each of the gas outlets to ensure an appropriate negativepressure is applied.

As discussed above, the reactor 212 includes four separate thermalreaction zones. The first thermal zone 254A includes the first four bandheaters and ends downstream and adjacent gas outlet 216; the secondthermal zone 254B includes the next 9 band heaters and ends downstreamand adjacent gas outlet 228; the third thermal zone includes the next 9band heaters and ends downstream and adjacent gas outlet 230A; thefourth thermal zone includes the next 5 band heaters and ends downstreamand adjacent gas outlet 230B. Thus, the number of band heatersassociated with the thermal zones is twenty seven. The last band heateris located downstream of gas outlet 230B, and this band heater isoperable to maintain the temperature of the char product above atemperature of 400° C. This is to prevent any VOCs that remain withinthe system (such as those entrained within the char product) fromcondensing into an oily residue that may adhere to, or otherwise form agunk in the reaction vessel, in moving parts associated with thereaction vessel (for example valves 234 or 236, or in any downstreamequipment.

During operation, thermal energy is applied to each thermal zone via thecorresponding band heaters to heat the rubber containing waste above thedegradation temperature of rubber which causes the generation ofvolatile gases and converts the rubber to the char product. Due to thetight tolerance between the edges of the screw auger 231 flighting andthe internal cylindrical surface of the reactor 212 a substantialportion of the volatile gases evolved in a given thermal reaction zoneare transported along with the rubber containing waste in a channelformed between successive flights of the auger 231. These gases aretransported through that thermal zone until they reach the portion ofthat thermal zone that includes the gas extraction pipe at which point asubstantial portion of those volatile gases is then withdrawn.

Each of the gas extraction pipes 216, 228, 230A and 230B feed into anexhaust manifold 320. In this particular case, the third and fourth gasoutlets 230A and 230B are merged into a single pipe 231 that is the samediameter as gas outlets 216 and 228 via Y-junction 230, and this singlepipe 231 feeds collective exhaust gas taken directly from gas outlets230A and 230B to the exhaust manifold 320. Due to this arrangement, thegas extraction system is a “tuned” system that balances the volumetricflow rates of gases through the various stages of the process. Gasextraction pipes 216, 228, 230A, and 230B are all of the same diameterand similar lengths. Given this, gas extraction pipes 216 and 228exhibit a pressure drop that is about the same, and as such, thevolumetric flow rate of gases taken off from gas extraction pipes 216and 228 is about the same. Whilst gas extraction pipes 230A and 230Balso have the same diameter as gas extraction pipes 216 and 228, pipes230A and 230B are connected via a Y-junction upstream of the extractionmanifold 320 and single pipe 231 (also of the same diameter as pipes216, 228, 230A, and 230B) feeds from the Y-junction into exhaustmanifold 320. Thus, the combined volumetric gas flow rate from pipes230A and 230B is about the same volumetric gas flow rate as for each ofpipes 216 and 228. In other words, the volumetric gas flow rate fromeach of pipes 230A and 230B is about half the volumetric gas flow ratethrough pipes 216 and 228. This “tuned” arrangement is beneficial as thelargest volumes of gas are generated in the first thermal reaction zone254A and the second thermal reaction zone 254B, whereas much lowervolumes of gas are typically generated in thermal reaction zones 254Cand 254D. Another advantage of the “tuned” gas extraction system is thatthe reduction in gas extraction flow rate at downstream thermal zones ofthe reactor reduces the carry over of dried carbon/char into the wastesystem.

The exhaust manifold 320 includes a temperature sensor 304 to monitorthe temperature of the withdrawn volatile gases. The manifold alsoincludes an outlet pipe 302 for feeding the volatile gases to acondenser. In some embodiments, the outlet pipe 302 also includes atemperature sensor.

FIG. 4 shows a cross section through and along the axis of the reactor212 illustrated in FIGS. 2 and 3. Notably, the orientation of the screwauger 231 can be seen within the reactor. FIG. 5 shows a cross sectionorthogonal to the axis of the reactor 212. Again, the position of thescrew auger 231 is illustrated. As can be seen there is minimalclearance space between the flight edges 502 and the internalcylindrical wall 504 of the reactor 212.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

EXAMPLE

Tables 1, 2, and 3 show the operating conditions used to convert a 50 mmclassified shredded tyre waste feed stock to a char product. TheseTables report data from a daily run sheet. In this case, 50 mmclassified shredded tyre waste including steel was fed into the reactor.The feed commenced at 06:30 and finished at 15:30. The residence time inthe reactor was 1 hour, with the initial outfeed exiting the reactor at07:30. Given the 1 hour residence time, the reactor was emptied at16:30. Table 1 reports a production total of 635 kg carbon, 246 kgsteel, and 600 L of oil.

Table 2 shows the temperatures measured at various points along thereactor denoted TC1-TC8 and G1-G7. FIG. 6 shows the positions oftemperature sensors TC1-TC7 on the top of the reactor 212 and adjacentto the exhaust manifolds. Note that TC8 is positioned in the finalexhaust manifold and is therefore not shown in FIG. 6. G1-G7 are alsotemperature gauges. These are positioned, as indicated in Table 2,within the bed of the reactor. Table 3 provides operational detailsacross the condenser.

TABLE 1 PRODUCTION Feed Stock 50 mm classified shredded tyre waste withSTEEL Used Carbon 635 Kgs Carbon Weight  95 88 100  97 100 95  60Produced Tally Steel 246 Kgs Steel Weight  43 10  68  69  56 ProducedTally Oil Produced 600 Liters Oil Start 950 Start 9000 Oil Finish 1000Finish 9600 Measurement Conversion Measurement Conversion Time KeepingThrough Time 1 Hours 0 Mins Infeed Infeed Projected Projected RubberInto Infeed Outfeed Produced Start Stop Outfeed Empty Time Amount TimeTemp 6.30 15.30 7.30 16.30 10.00 500  8.40 35 11.35 550 10.00 30 14.40550 11.15 33 12.40 38 14.00 42 15.45 33 16.30 33

TABLE 2 300 400 440 455 475 400 220 @TC2 BETWEEN @TC3 BETWEEN @TC4 @TC5@TC6 Time TC1 TC2 TC3 TC4 TC5 TC6 TC7 TC8 G1 G2 G3 G4 G5 G6 G7 6.30 260257 363 451 419 328 88 76 445 460 405 590 500 450 350 7.00 269 265 373453 432 341 98 76 445 465 410 580 500 470 370 7.30 270 269 376 455 437362 135 75 430 450 400 550 485 470 405 8.00 270 269 372 455 433 376 16274 420 430 390 540 475 450 420 8.30 271 270 367 454 423 373 183 74 420420 385 540 475 435 410 9.00 273 270 363 454 418 363 191 74 420 405 380540 475 430 400 9.30 277 271 361 455 416 357 195 73 420 400 380 540 475430 390 10.00 280 271 359 455 420 360 197 73 415 395 375 540 475 445 39510.30 282 270 355 453 421 361 202 72 415 390 370 530 475 435 400 11.00284 270 352 452 416 359 203 72 415 390 370 530 475 430 390 11.30 284 268349 450 417 361 204 72 405 380 355 525 465 440 400 12.00 284 266 345 447413 360 208 71 400 375 350 520 460 425 390 12.30 283 267 341 444 408 357208 71 410 375 355 520 460 425 390 13.00 283 268 340 446 413 361 206 71405 375 350 520 460 430 395 13.30 282 268 339 446 413 360 206 71 400 370350 520 460 425 395 14.00 281 267 337 444 407 358 206 71 420 375 350 520455 425 390 14.30 284 273 346 456 419 360 193 72 440 400 375 550 480 450390 15.00 287 275 352 455 425 361 197 72 430 400 375 540 475 445 40015.30 289 273 351 454 421 359 201 72 420 395 370 530 475 435 400 16.00291 276 354 453 418 360 203 72 445 420 380 540 475 435 395 16.30 265 275346 432 433 364 192 72 415 410 375 510 470 470 400

TABLE 3 MANOMETER TEMPERATURES COND COND COND COND AFTERBURNER EXT 1 INOUT IN OUT OUTFEED SPACER WATER TEMP FAN % −0.01 −0.03 −0.03 11 10 13 813 −0.01 −0.03 −0.03 25 10 15 9 16 −0.02 −0.02 −0.09 67 14 37 14 15−0.01 −0.01 −0.10 93 16 57 22 18 −0.02 −0.08 −0.11 107 19 72 29 21 −0.03−0.10 −0.09 108 21 77 34 23 −0.04 −0.06 −0.06 108 22 78 37 23 −0.02−0.08 −0.09 108 23 82 41 22 −0.02 −0.08 −0.08 113 25 84 45 26  0.00−0.09 −0.09 112 25 87 47 26 −0.01 −0.11 −0.12 115 27 89 50 28  0.00−0.09 −0.11 123 27 96 53 26 1076 18.5 100% −0.03 −0.05 −0.06 117 28 9157 29 1144 10 100%  0.00 −0.12 −0.12 114 28 86 57 28 1339 19 100% −0.01−0.08 −0.10 121 29 98 56 27 1371 19.5 100% −0.01 −0.05 −0.07 121 30 9259 24 1395 22.5 100% −0.01 −0.05 −0.06 95 29 74 55 30 1298 9 100% −0.06−0.12 −0.14 104 29 75 55 29 1310 15  25%  0.00 −0.17 −0.18 113 29 84 5332 1238 15  25% −0.05 −0.14 −0.14 116 30 84 57 29 1100 15  25% −0.03−0.02 −0.02 90 29 73 52 29 723 25  0%

1. A process for the non-oxidative thermal degradation of a rubbercontaining waste including: feeding the rubber containing waste throughan inlet and into a hermetically sealed cylindrical flow-through reactorhaving a heating zone, a cooling zone, and one or more thermal treatmentzones arranged along a horizontal axis of the reactor between the inletand the outlet of the reactor, wherein the one or more thermal reactionzones are located between the heating zone and the cooling zone, whereinthe heating zone is located upstream of the one or more thermal reactionzones and the cooling zone is located downstream of the one or morethermal reaction zones, wherein an axial reactor length of thehorizontal axis of the reactor is less than about 40 ft, and whereineach thermal reaction zone is provided with: one or more heatingelements controllable to heat the thermal reaction zone to an operatingtemperature for mediating the non-oxidative thermal degradation ofrubber in the rubber containing waste, and one or more gas outlets forwithdrawing gas or gases evolved during the non-oxidative thermaldegradation of the rubber; pre-heating the rubber containing waste inthe heating zone to a temperature below the degradation temperature ofthe rubber containing waste prior to transporting the rubber containingwaste through the one or more thermal reaction zones; operating one ormore thermal reaction zones at a temperature at or above the thermaldegradation temperature of rubber, operating a screw auger in both theforward and reverse directions to agitate the rubber containing wastewithin the reactor and to transport the rubber containing waste alongthe horizontal axis of the reactor, and through the reactor at a rate toprovide: a residence time in the one or more thermal reaction zonessufficient to heat the rubber containing waste to a temperature abovethe degradation temperature of rubber, and to degrade rubber in therubber containing waste into a volatile gas or gases, fuel oil and achar product, and a residence time in the reactor of less than 2 hours,wherein flighting on the screw auger tracks the internal cylindricalsurface of the reactor in close relationship to minimise or prevent thetransport of the volatile gas or gasses and/or the char product througha clearance space between outer edges of the flighting and the internalcylindrical surface of the reactor; cooling the char product in thecooling zone to a temperature below the degradation (pyrolysis)temperature of the rubber containing waste and sufficient to preventcondensation of any volatile organic compounds (VOCs) that have not beenextracted into a liquid and produce a dry char residue product prior todischarging the char product from the reactor; and applying a negativepressure to each thermal treatment zone and the cooling zone to withdrawvolatile gas or gasses that are formed in that thermal treatment zonefrom the non-oxidative thermal degradation of the rubber; dischargingthe char product through the outlet of the reactor.
 2. The process ofclaim 1, wherein the volatile gas or gases include limonene.
 3. Theprocess of claim 1, wherein the reactor includes: at least two thermalreaction zones including: the first thermal reaction zone including oneor more first heating elements, the one or more first heating elementscontrollable to heat the first thermal reaction zone to a firstoperating temperature, and a second thermal reaction zone including oneor more second heating elements, the one or more second heating elementscontrollable to heat the second thermal reaction zone to a secondoperating temperature different to the first operating temperature; theprocess further including: operating the first thermal reaction zone atthe first operating temperature, the first operating temperaturesufficient to form a first volatile gas or gases, and operating thesecond thermal reaction zone at the second operating temperature, thesecond operating temperature being higher than the first operatingtemperature, to enhance the conversion of the rubber to the char productand from a second volatile gas or gases.
 4. The process of claim 1,wherein the rubber containing waste in the one or more thermal reactionzones is heated to a temperature of from 445° C. and up to 550° C. 5.The process of claim 4, wherein the rubber containing waste in the oneor more thermal reaction zones is heated to a temperature of from 460°C. and up to 500° C.
 6. The process of claim 1, wherein the cooling stepcomprises cooling the char product to a temperature of no less thanabout 400° C. prior to discharging the char product from the reactor. 7.The process of claim 1, wherein the pre-heating step comprises heatingthe rubber containing waste in the heating zone to a temperature of atleast about 300° C.
 8. The process of claim 3, wherein the firstvolatile gas or gases is a sulfur gas or sulfur containing gas.
 9. Theprocess of claim 3, wherein the second volatile gas or gases issubstantially free of sulfur.
 10. The process of claim 3, wherein thesecond volatile gas or gases comprise limonene.
 11. The process of claim1, wherein the process further includes feeding the rubber containingwaste through the inlet via an inlet air lock chamber located upstreamof the inlet.
 12. The process of claim 1, wherein the process furtherincludes discharging the char product from the outlet and into an outletair lock chamber.
 13. The process of claim 1, wherein flighting on thescrew auger tracks the internal cylindrical surface of the reactor inclose relationship such that the clearance space is 7 mm or less. 14.The process of claim 1, wherein the rubber containing waste is shreddedtyre waste including at least rubber, steel and nylon.
 15. The processof claim 3, wherein the first volatile gas is withdrawn at a volumetricflow rate from 1.1 to 3 times the second volatile gas volumetric flowrate.
 16. The process of claim 1, where the residence time of the rubbercontaining waste in the heating and cooling zones is less than theresidence time in the thermal reaction zone.
 17. The process of claim 1,wherein the rubber containing waste is converted into about 39% carbon,about 15% steel and about 34% tire derived oil.
 18. The use of ahermetically sealed flow-through reactor to thermally degrade a rubbercontaining waste, the hermetically sealed flow-through reactor having aninternal cylindrical surface, and the reactor including: an inlet and anoutlet, a heating zone, a cooling zone and one or more thermal reactionzones, wherein the one or more thermal reaction zones are arranged alonga horizontal axis of the reactor between the heating zone and thecooling zone and between the inlet and the outlet, wherein the heatingzone is located upstream of the one or more thermal reaction zones andthe cooling zone is located downstream of the one or more thermalreaction zones, wherein an axial reactor length of the horizontal axisof the reactor is less than about 40 ft, and wherein each thermalreaction zone is provided with: one or more heating elementscontrollable to heat the thermal reaction zone to an operatingtemperature for mediating the non-oxidative thermal degradation ofrubber in the rubber containing waste, one or more gas outlets with eachof the one or more gas outlets being connected to an extraction pipe forwithdrawing gas or gases evolved during the non-oxidative thermaldegradation of the rubber; and a screw auger located within the reactor,the screw auger configured to rotate in both the forward and reversedirections to agitate and transport the rubber containing waste throughthe one or more thermal reaction zones in both the forward and reversedirections and to the outlet such that the resisdence time in thereactor is less than 2 hours, wherein flighting on the screw augertracks the internal cylindrical surface of the reactor in closerelationship to minimise or prevent the transport of material through aclearance space between outer edges of the flighting and the internalcylindrical surface of the reactor; the heating zone is operated so asto pre-heat the rubber containing waste to a temperature lower than thethermal degradation temperature of the rubber containing waste prior totransporting the rubber containing waste through the one or more thermalreaction zones; and the cooling zone is operated so as to cool the charproduct to a temperature below the degradation (pyrolysis) temperatureof the rubber containing waste and sufficient to prevent condensation ofany volatile organic compounds (VOCs) that have not been extracted intoa liquid and produce a dry char residue product, prior to dischargingthe char product from the reactor and wherein the cooling zone comprisesone or more gas outlets for withdrawing gas or gases.